The present invention relates to two component compositions capable of forming polyurethane sealants.
Polyurethanes are well known thermoplastic polymers which, as is known, can be made thermosetting. Such polymers are produced by the condensation reaction of a polyisocyanate and a hydroxyl-containing material, usually a polyol derived from propylene oxide or triclorobutylene oxide. Because of the good resistance, when cured, to abrasion, weathering, and solvents, they are utilized as sealants, caulking agents, and adhesives in a variety of uses, including architectural uses such as control and expansion joints in concrete floors, sidewalks, parking decks, industrial floors, other areas exposed to pedestrian and/or vehicular traffic, and sealing wood and metal structural components.
In making thermoset curable, polyurethane resins, it is conventional to use two component compositions in which a diisocyanate prepolymer forms one component and the polyol the second component, such polyol second component, including a catalyst or curing agent. Among the most useful curing agents are the organo-mercuro catalysts. However, the use of such mercury catalysts is undesirable because of their toxicity and potential adverse environmental impact. Also, their use is restricted by EPA regulations to exterior applications and there are possible future restrictions and even banning the use thereof.
Also, at the present time many of the compositions utilized for architectural purposes have a residual tack, which is undesirable in architectural usages, particularly since it permits debris and other matter to adhere to the polyurethane as it is curing.
A further problem with two component polyurethane thermoset curing compositions is the fact that many of them do not have a suitable pot life. In some instances the two components, when admixed, will result in a product which will cure within a very short period of time, making it unsuitable for use in construction where longer pot life is necessary when admixing large quantities of sealant that have to be applied to the structure and require a long application time.
Efforts to try to substitute other metal salts such as dibutyltindilaurate, bismuth neodecanoate, combinations of bismuth and zinc octoate, lead octoate, bismuth octoate and stannous octoate have not proven satisfactory. Mercury catalysts are selective and do not catalyze water-isocyanate reaction. Surface tack is probably due to water (atmospheric moisture) reaction with isocyanate. The result is a stoichiometric imbalance on the surface. This being the case, catalysts that catalyze the water-isocyanate reaction in addition to the polyol-isocyanate reaction should make the surface tack worse. This is the case when dibutyltindilaurate or a tertiary amine such as triethylenediamine is used.